This invention relates to a shallow vessel for use on a coating line for meniscus coating one surface of a metal strip. More particularly, the invention relates to means for inductively heating molten coating metal contained in the vessel and means for concentrating the magnetic flux of the induction heater.
Conventional hot dip coating requires a metal strip to be immersed into a bath of molten metal. The immersion process generally requires a large vessel for containing molten metal having a depth of about two meters or more. It is well known to inductively heat molten metal while being contained within such large refractory lined vessels. It also is known to inductively heat such molten metal when being pumped or flowed through a refractory lined conduit. An induction coil may be disposed annularly with respect to the vessel or conduit either within the refractory lining or outside the vessel.
In recent years, techniques have been developed to coat one or both sides of metal strip with molten metals using a meniscus. U.S. Pat. No. 4,557,953 discloses horizontal meniscus coating one side of a steel strip. A cleaned strip is passed from a sealed snout to a large coating pot containing molten metal. Deflection rolls are used to pass the strip sufficiently close to the molten metal surface so that molten metal wets the lower surface of the strip and is withdrawn from the pot onto the surface of the strip.
U.S. patent application Ser. No. 07/803,278 filed Dec. 4, 1991; incorporated herein by reference, discloses vertical meniscus coating one or both sides of a steel strip using a horizontally disposed shallow vessel for containing molten metal. The vessel includes a departure lip mounted on the upper surface of one side of the vessel. The level of molten metal is maintained in the vessel relative to the upper elevation of the departure lip so that an uninterrupted flow of the molten metal can be delivered over the departure lip to a surface of the strip as the strip travels vertically past the departure lip. This patent application discloses that means for heating the departure lip may be provided to prevent freezing of the molten metal as it flows over the departure lip. The heating means may be in thermal contact with the departure lip or may be immersed into the molten metal bath.
Nevertheless, there remains a need for being able to heat molten metal contained within a relatively shallow vessel. There also remains a need for a heating means to maintain a uniform temperature of the molten metal contained within a shallow vessel.